Study Guide: Computer Codes

1. Binary-Coded Decimal (BCD)

BCD is a coding system that represents decimal numbers (0-9) in binary form. Each decimal digit is represented by a 4-bit binary equivalent.

Key Features:

1. Each digit of a decimal number is converted to its binary equivalent separately.

2. For example:

1. Decimal 5 in BCD is 0101.

2. Decimal 25 in BCD is 0010 0101 (two separate 4-bit groups).

Advantages:

1. Easy conversion between human-readable decimal numbers and machine-readable binary.

2. Commonly used in calculators and digital displays.

Disadvantages:

• Inefficient compared to pure binary; it requires more bits to represent the same value.

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2. American Standard Code for Information Interchange (ASCII)

ASCII is a character encoding standard used for representing text in computers and electronic devices. Each character (letters, numbers, symbols) is assigned a unique 7-bit or 8-bit binary code.

Key Features:

1. Standard ASCII uses 7 bits, allowing for 128 characters.

1. Example:

1. 'A' = 1000001 (Decimal 65)

2. 'a' = 1100001 (Decimal 97)

2. Extended ASCII uses 8 bits, allowing for 256 characters, supporting additional symbols and foreign language characters.

Applications:

• Widely used in programming, text files, and data communication.

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3. Gray Code

Gray code is a binary numeral system where two successive values differ in only one bit. It is also called "reflected binary code."

Key Features:

1. Minimizes errors during transitions in digital systems.

2. For example:

1. Decimal 0-3 in binary: 00, 01, 11, 10 (Gray Code).

Applications:

• Used in position encoders, digital logic circuits, and error correction.

Conversion to Binary:

• Can be converted to/from binary using specific algorithms.

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4. Excess-3 Code

Excess-3 is a non-weighted code used to express decimal numbers. It is obtained by adding 3 (0011 in binary) to the decimal number and then converting the sum to binary.

Key Features:

1. Decimal 0 is represented as 0011 (0+3).

2. Decimal 9 is represented as 1100 (9+3).

Advantages:

1. Eliminates issues like "end-around carry" in digital systems.

2. Provides a self-complementary feature, which simplifies arithmetic operations.

Applications:

• Used in digital clocks, calculators, and error correction in some digital systems.

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Comparison of the Codes

Code	Purpose	Bits per Unit	Applications
BCD	Decimal representation in binary	4 bits per digit	Calculators, digital displays
ASCII	Character encoding	7 or 8 bits	Text files, data communication
Gray Code	Minimize transition errors	Variable	Encoders, digital logic circuits
Excess-3 Code	Decimal correction and representation	4 bits per digit	Clocks, calculators, error correction

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Summary:

Understanding these codes is fundamental in computer science and digital electronics. They provide the foundation for various encoding, storage, and communication processes in computing systems. Familiarity with their structure and applications is essential for both theoretical learning and practical implementation.